Above-referenced U.S. Pat. No. 4,851,095, entitled MAGNETRON SPUTTERING APPARATUS AND PROCESS, issued Jul. 25, 1989, from application Ser. No. 154,177 filed Feb. 8, 1988, to inventors Scobey, Seddon, Seeser, Austin, LeFebvre, and Manley (also referred to as the Scobey, Seddon et al '095 patent or, simply, the '095 patent) discloses several embodiments of a vacuum deposition and reaction system which provides enhanced control of the thickness of optical thin films deposited on curved substrates such as tubes in a vacuum processing chamber. The '095 patent is hereby incorporated by reference in its entirety.
The system disclosed in the '095 patent incorporates a planetary drive substrate support and translation system in which (1) tubular substrates (workpieces) such as lamp bulbs or (2) cylindrical substrate supports are mounted for rotation at the circumference of a rotatable drum (or cage). One or more process (deposition and reaction) zones are spaced along the circumference of the drum.
In order to ensure reaction, e.g., oxidatior of the entire thickness of material deposited during each pass in front of the associated deposition device, the deposited layer is limited to about 5 Argstroms per pass and the exposure to the deposition and reaction zones must correspond closely. (By way of example in this patent document, we refer to the use of sputtering targets in the reaction zones and oxidizers in the reaction zones, with the understanding that other deposition and reaction devices can be used.) This objective has been achieved by rotating the substrates through an integral number of revolutions in front of the sputtering target(s) and the oxidizer.
Even a single rotation of the main drive requires several revolutions of the substrate. Consequently, consistent with these requirements, the gear ratio between the main (sun) drive shaft or spindle and the planetary substrate spindles has been selected to provide a planetary rotation speed which is much faster than the associated rotation of the main drive. For example, in one application, drum rotation of about 60 rpm effects substrate rotation of about 1,000 rpm.
In addition, the relatively high-rate planetary rotation of a substrate such as a tube is used to effect uniform film deposition around the circumference of the substrate. Similarly, uniform circumferential deposition is promoted when individual substrates are mounted around the circumference of a planetary rotating support mounted on a sun drum or cage. In both cases, axial deposition uniformity (uniformity parallel to the axis of rotation of the drum or cage) is promoted by using an axially uniform deposition source such as a linear magnetron sputter deposition device which is mounted parallel to the axis of rotation of the drum and to the planetary axis of rotation.
Despite the many advantages provided by the apparatus and methods disclosed in the '095 patent, like all things invented by man, such apparatus and methods are susceptible to improvement. In this case, the high rotation speeds and the power required to drive the planetary gear system at very high rotation speeds may result in heat dissipation in the rotary motion and bearings sufficient to degrade the system, for example, by overheating the bearings, and the process carried out in the chamber. In addition, the fast rotation in the presence of abrasive optical materials such as silicon oxide, tantalum oxide and/or titanium oxide, which are formed by the various processes practiced using the chamber, may cause wear of the many system bearings. As a result, the system may require maintenance and/or parts replacement sooner than would otherwise be necessary.